<jsp:useBean>的用法，最好有例子说明，请各位专家指点指点！

Question

<jsp:useBean id="prin" class="prin" scope="page"/>类的构造函数呢？
public class  prin
{public prin(){
}public  void pr() 
{
 System.out.println("Hello World!");
}
}

Answer 1

修改成:
<%@page import="prin"%>
<jsp:useBean id="prin" class="prin" scope="page">
</jsp:useBean>
<% prin.pr %>public class  prin
{
public prin(){
}
public  void pr() 
{
 System.out.println("Hello World!");
}
}
错误信息:
HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException: Unable to compile class for JSPAn error occurred at line: 6 in the jsp file: /test1.jspGenerated servlet error:
    [javac] Compiling 1 source fileD:\tomcat\work\Standalone\localhost\_\test1_jsp.java:61: ';' expected
      out.write("\r\n");
         ^
D:\tomcat\work\Standalone\localhost\_\test1_jsp.java:60: cannot resolve symbol
symbol  : class pr  
location: class prin
 prin.pr 
     ^An error occurred at line: -1 in the jsp file: nullGenerated servlet error:
D:\tomcat\work\Standalone\localhost\_\test1_jsp.java:61: out is already defined in _jspService(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
      out.write("\r\n");
      ^
3 errors
at org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:130)
at org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:293)
at org.apache.jasper.compiler.Compiler.generateClass(Compiler.java:353)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:370)
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:473)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:190)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:295)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:256)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2416)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:223)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:601)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:392)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:565)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:619)
at java.lang.Thread.run(Thread.java:479)--------------------------------------------------------------------------------

Answer 2

<%@page import="prin"%>   //这个也可以不要
<jsp:useBean id="prin" class="com.prin.Prin" scope="page"/>
</jsp:useBean>  //不要这个删掉
<% prin.pr() %> //调方法啊不是属性啊 
package com.prin;
public class  Prin //类名大写大哥
{
public prin(){      //默认构造
}
public  void pr()       
{
 System.out.println("Hello World!");
}
}

Answer 3

sorry ，构造函数大写 public Prin(){      //默认构造
}

Answer 4

<jsp:useBean id="prin" class="com.prin.Prin" scope="page"/><%prin.pr(); //分号%>

Answer 5

谢谢您的批评指导，再帮帮我!package com.prin;
public class  Prin 
{
public Prin(){
}
public  void pr()       
{
 System.out.println("Hello World!");
}
}
用javac编译时会有一个错误

Answer 6

test.java:2: class Prin is public, should be declared in a file named Prin.java
public class  Prin
       ^
1 error
这个？〉 重命名你的java文件改大写啊，Prin.java

Answer 7

编译通过
<jsp:useBean id="Prin" class="com.prin.Prin" scope="page"/>
<% Prin.pr(); %> //调方法啊不是属性啊 
package com.prin;
public class  Prin 
{
public Prin(){
}
public  void pr()       
{
 System.out.println("Hello World!");
}
}还是会出错

Answer 8

TO:thefishwilldie(我不懂啊！！！) 
请您再指点指点，我也在跟着学！

Answer 9

<jsp:useBean id="prin" class="com.prin.Prin" scope="page"/><%prin.pr(); //分号%>

Answer 10

HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException: Unable to compile class for JSPAn error occurred at line: 0 in the jsp file: /test1.jspGenerated servlet error:
    [javac] Compiling 1 source fileD:\tomcat\work\Standalone\localhost\_\test1_jsp.java:41: cannot resolve symbol
symbol  : class Prin  
location: package prin
      com.prin.Prin Prin = null;
              ^An error occurred at line: 0 in the jsp file: /test1.jspGenerated servlet error:
D:\tomcat\work\Standalone\localhost\_\test1_jsp.java:43: cannot resolve symbol
symbol  : class Prin  
location: package prin
        Prin = (com.prin.Prin) pageContext.getAttribute("Prin", PageContext.PAGE_SCOPE);
                        ^An error occurred at line: 0 in the jsp file: /test1.jspGenerated servlet error:
D:\tomcat\work\Standalone\localhost\_\test1_jsp.java:46: cannot resolve symbol
symbol  : class Prin  
location: package prin
            Prin = (com.prin.Prin) java.beans.Beans.instantiate(this.getClass().getClassLoader(), "com.prin.Prin");
                            ^
3 errors
at org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:130)
at org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:293)
at org.apache.jasper.compiler.Compiler.generateClass(Compiler.java:353)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:370)
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:473)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:190)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:295)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:256)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2416)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:223)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:601)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:392)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:565)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:619)
at java.lang.Thread.run(Thread.java:479)--------------------------------------------------------------------------------

Answer 11

TO:thefishwilldie
是不是我的配置有问题
我的系统配置：win2000+tomcat4.1+jdk.1.3.1+EditPlus 2
我的web目录：    D:\tomcat\webapps\ROOT  （test1.jsp)
我的classes目录：D:\tomcat\webapps\ROOT\WEB-INF\classes （prin.class)

Answer 12

classes目录要把路径加上 变成这样
 D:\tomcat\webapps\ROOT\WEB-INF\classes\com\prin\Prin.class

Answer 13

我们就用JBuilder搞.什么都不用调了...(对小程序来说..)

Answer 14

非常感谢您的指点（thefishwilldie）
我成功了！to: Unicorn008(菜之鸟) 我是想学该方法！谢谢您的题点！